High-frequency coupling device



y 1948. P. c. GARDINER 2,446,003

HIGH-FREQUENCY COUPLING DEVICE Filed Nov. 12, 1946 Figl.

T0 5 5, 8 v T0 OSCILLATOR TDOSCILLAT Inventor: Paul C. Gardiner;

. His Attorney.

Patented July 27, 1948 2,446,003 HIGH-FREQUENCY COUPLING navrca Paul C. Gardiner, Scotla, N. Y., assignor to General Electric Company, a corporation of New York Application November 12, 1946, Serial No. 709,393

8 Claims. 1

My invention relates to a high frequency coupling device and particularly to a coupling transformer and associated switching means suitable for multi-band operation at ultra-high frequencies.

In the past, band-switching at ultra-high frequencies, for example of the order of 200 megacycles and above, has presented particular difllculties. At such frequencies the physical dimensions of inductive coupling units become quite small and large variations in frequency may be caused by relativel minute changes in the circuit paths or contact resistance. In particular, commercial tolerances in band-switches are generally such that the moving contact parts cannot always be depended upon to reseat in exactly the same position with repeated operation of the switch. This has been found to cause appreciable frequency variations. Similar variations may also result from relatively slight flexure of the coupling coils and lead connections to the bandswitch. Another diiiiculty arises from the fact that, if band-switching is accomplished by shortcircuiting a portion of the coupling inductances, the loading effect of short-circuited turns becomes substantial at these high frequencies.

It is an object of my invention to provide an improved coupling device tunable to at least two different frequency bands at ultra-high frequencies which requires a minimum of switching elements and is stable in operation.

It is a further object of my invention to provide an improved multi-band coupling transformer with switching means for changing the effective coil inductance in a very simple manner, so constructed and arranged that small variations in the switch contact positions, such as may normally be encountered in commercial tolerances, have negligible effects upon frequency.

It is still another object of my invention to provide an improved inductive coupling device for high-frequency circuits and the like which utilizes a coupling loop of special configuration so that one portion of the loop may be short-circuited for operation over a higher frequency band, with minimum loading effect from the short-circuited portion.

It is still another object of my invention to provide an improved multi-band coupling transformer, suitable for operation at ultra-high frequencies, which is simple and rugged mechanically and highly stable electrically.

The features of my invention which I believe to be novel are set forth with particularity in the appended claims. My invention itself, however,

together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawing, in which Fig. 1 is a schematic circuit diagram of a high frequency, push-pull converter circuit showing one application of the improved coupling device embodying my invention; Fig. 2 is a perspective view illustrating one form of mechanical construction for the circuits of Fig. 1, in which certain conventional circuit connections have been indicated only schematically to simplify the view; and Fig. 3 is a fragmentary side elevation of an alternative form of switch contact construction that may optionally be employed in the structure of Fig. 2. Corresponding reference numerals have been applied to corresponding elements in the several figures of the drawing.

In the drawings, the invention is shown in one application to the converter stage of an ultrahigh frequency super-heterodyne receiver, although it is applicable to many other types of inductively-coupled circuits. Radio frequency input signals are supplied to the primary winding 8 of the coupling transformer, the secondary winding 9 of which is connected at its terminals 10 and II through coupling capacitors l2 and I3 to the control grids of a dual amplifier tube I 4'. Tube H is illustrated as comprising a pair of triode elements connected in a conventional push-pull circuit, the details of which are familiar to those skilled in the art and which form no part of my invention. As shown, suitable negative bias potentials are supplied to the grids from the bias source [5 through resistors l6 and I1. Local oscillations are supplied to the grid from a local oscillator (not shown) through conductor l8 and capacitors l9 and 20. The anodes of the triode sections are connected to the primary of the output coupling transformer 2| which is centertapped for connection to a suitable source of anode operating potential, indicated by the conductor 22 connected to B+. The intermediate frequency signals are then supplied to succeeding intermediate frequency amplifiers from the secondary winding 23 as is well understood in the art.

In accordance with my invention, the secondary winding 9 of the coupling transformer is given a special configuration. As shown, it consists of a single elongate, closed loop connecting the terminals l0 and H. Near the center portion 9a of the loop, both sides are deformed toward the major axis of the loop to provide reentrant portions with a relatively small spacing between opposite sides of the loop. On either side of the pertions 9a the loop is formed into approximately circular sections 9b and 90, each of which incloses a substantial area as compared to the area between the conductors at the contiguous center, portion 9a.

As shown in Fig. 2, both of are preferably in the form of flat loops lying in the same plane. The conductors should be relatively stiff and may be rigidly mounted on stand-ofl insulators 24 on a supporting panel 25. The converter tube I4 may also .be mounted on similar insulators 24, with the tube base 26 located close to the terminals Ill and H so as to permit as short connections as possible. The primary loop 8 is the windings 8 and 8 also preferably locatedsymmetrically with respect to the portions 9b and 9c of the secondary loop so as to be in the same inductive relationship to each of them.

For band-switching, means are provided for selectively short-circuiting the secondary loop across the narrow portion 9a. The exact construction and arrangement of the switching means is not critical. As shown in Figs. 1 and 2 of the drawing, it comprises two curved spring members 30 and 3! connected to opposite sides of the loop respectively. These springs are normally out of contact with each other and are forced into conducting engagement by the insulated cam 32 actuated by the control knob 33. Other alternative switching arrangements will readily occur to those skilled in the art. For example, an alternative construction is shown in Fig. 3 in which a single spring leaf 34 may be rotated so as to bridge the gap between the conductors, as shown in the solid line position, or

- rotated to a position 90 from the first positions so as to be out of contact with the loop, as indicated by the dotted outline 34a. Another possible alternative would be to provide a small metal plug which could be selectively inserted to effect the short circuit. The important thing is that in all cases the switch element should make good electrical contact and the pressure on the contacts should not be suflicient to flex the loop conductor appreciably.

It will now be seen that when the short-circuiting switch'is open, the entire loop 9 is activelyin circuit. When the short-circuiting switch is closed, only the right hand portion 91) of the loop is effective, tuning the transformer to a higher frequency band.

Since the length of the short-circuiting path through the switch contacts across the portion 9a is relatively short as compared to the length of the entire loop portion 9b, I have found that minute contact variations, such as will normally occur in the positioning of the contact elements during successive switching operations, have no serious effect upon the operating frequencies.

As a second important feature of my invention, it will be noted that the effect of the shortcircuited turn, formed by the loop portion 90 when the shorting switch contacts are closed, has minimum loading efiect upon the active portion 9b because of its relative physical position on the opposite side of the short circuiting point along the major axis of the loop.

Although the coupling device of my invention is not limited to any particular frequency range, circuit dimensions for one particular application will be of interest. In a circuit designed to operate either in the vicinity of 200 me. or 400 mc., the diameters of the circular portions 9b and 90 were approximately of an inch, the spacing between the approximate centers of these portions was about two inches and the distance between the loop conductors at the reduced portion Ila was about of an inch. It was found that the loading efiect of the portion 80 when short circuited was negligible for practical purposes and. .,th a t nearly the same voltage .gains could be realized for the I converter in both? of ithe frequency ranges.

While I have shown a particular embodiment of my invention, it will of course be understood that I do not wish to be limited thereto since various modifications may be made. For example, in some applications, it may be desired to have more than one reduced intermediate loop portion and corresponding shorting switches across each of them to cover more than two frequency ranges. I therefore contemplate by the appended claims to cover these or any other modifications as fall within the true spirit and scope of my invention.

What I-claim as new and desire to secure by Letters Patent of the United States is:

1. An inductive coupling device for high frequency apparatus and the like comprising spaced primary and secondary windings, one of said windings comprising a single loop conductor enclosing at least two substantial areas with a relatively narrow contiguous area between them, and means for selectably shorting said conductor across said narrow area.

2. A multi-band coupling transformer for high frequency apparatus and the like comprising spaced primary and secondary windings, said secondary winding consisting of a one-turn loop, said loop having a reentrant portion intermediate its ends so that opposite sides of the loop are relatively close together at said reentrant portion as compared to portions of said loop on either side thereof, a two-position switch for selectably shorting said loop across said reentrant portion, whereby substantially said entire loop is effective for one band and only a portion of saidloop is effective for a second band.

3. A high frequency coupling transformer having one winding in the form of a one-turn elongate loop connecting two adjacent terminals, said loop having a doubly-reentrant intermediate portion and being so shaped as to enclose two approximately circular areas with a relatively narrow contiguous area between them, a two-position switching means for selectably making a conductive connection across said reentrant portion, whereby in one position substantially all the area enclosed by said loop is effective between said terminals and in the second position only the adjacent area is effective, the short-circuited turn enclosing the other area in said second position being disposed so as to have minimum loading effect.

4. A multi-band coupling transformer for high frequency apparatus and the like comprising a first winding in the form of a substantially planar, elongate, one-turn, loop conductor, said conductor being deformed inwardly near the midportion of the loop so as to bring opposite sides of the loop relatively close together as compared to portions lying on either side of said mid-portion, selectively operable means for shorting said loop at said midportion, and a second winding inductively coupled to said first winding.

5. A dual-band high-frequency coupling device having two inductively coupled windings, one winding consisting of a substantiallyjlat, singleturn, elongate, loop conductor connected between two adjacent terminals, both sides of said loop being bent inwardly so as to bring opposite sides of said loop into relatively narrow spacing near its center portion and to form two approximately circular loop sections lying on either side thereof, electrical switching means for selectively making a conductive connection across said narrowed center portion to short-circuit one of said loop sections, the inductance of the other section being largely free from loading effects of said one section when short-circuited, or effects due to minute variations in the length of said conductive connection.

6. A coupling device for high-frequency apparatus and the like comprising two inductively coupled windings, one of said windings consisting of an elongate, single-turn, conducting loop, at least one portion of said loop intermediate its ends having relatively close spacing between sides of the loop as compared to other portions, and means for selectively establishing a direct conductive connection across said intermediate portion.

7. A dual-range coupling device for high-frequency apparatus and the like comprising two inductively coupled windings, one of said windings consisting of an elongate, single-turn, closed, conducting loop connected at its ends to a pair of adjacent terminals, the sides of said loop first diverging from said terminals, then converging to a relatively narrow spacing at an intermediate portion, and then diverging again before closing said loop, and means for selectively establishing a shorting path across said intermediate portion, whereby when said path is established small variations in the length of said path have negligible efiect upon the inductance of the active portion of the loop lying between said path and said terminals.

8. A coupling device for high-frequency apparatus and the like comprising two inductively coupled windings, one of said windings consisting of an elongate, single-turn substantially flat, conducting loop, opposite sides of said loop having non-uniform spacing from a major axis of symmetry of said loop, said opposite sides being relatively close to said axis at least at one intermediate point as compared to their spacings at other points along said axis and means for selectively establishing a conductive connection between opposite sides of said loop at said intermediate point.

PAUL C. GARDINER.

REFERENCES CITED The following references are of record in the tile of this patent:

UNITED STATES PATENTS 

